When there was first the EW/MW/LW split, if I recall correctly there was little overlap in the plane sets. 109E's, for example, were not in service by "Late War" and so they were not available in the LWA. A lot of people, myself included, thought that was a bad idea, and there was enough of a clammor to change it that we ended up with all planes being available in the LWAs.
In hindsight, though, I wonder if that was ultimately counterproductive. If the plane sets in the time frames were unique, would those arenas have more appeal? Would a LW arena where the only planes available were those still in service in 1945 have less appeal (and therefore spread the numbers)? I think so, but I am less certain that the net effect would be players switching arenas rather than complaining about it.
EW also has a problem with the plane set in that there are really not enough EW rides. Add a few French fighters, Cr42s, Gladiators, etc, and does it become more used? I think it would, but maybe not if they were also available in the LWAs.